1. Field of the Invention
The present invention relates to a vibratory meter, and more particularly, to a method and apparatus for a vibratory meter.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flow meters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that contains a material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flow meter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries, emulsions, and the like, in the system. Each conduit may be viewed as having a set of natural vibration modes, including for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations. Two such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to electronic instrumentation. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement, among other things. Vibratory meters, including Coriolis mass flow meters and densitometers, therefore employ one or more flow tubes that are vibrated in order to measure a fluid.
The techniques by which the vibrating Coriolis flow meters, measure parameters of a flowing material are well understood; see, for example, U.S. Pat. No. 6,505,131, the disclosure of which is hereby incorporated herein by reference; therefore, a detailed discussion is omitted for brevity of this description.
In vibrating Coriolis flow meters, the amplitude of the Coriolis deflections is considerably less than the amplitude of the flow tube drive frequency vibrations. Even though the amplitude of the Coriolis deflections is relatively small, it is the Coriolis deflections in the flow tube vibrations that generate the pick-off output signals that are processed by meter electronics to determine the mass flow rate and other parameters of the flowing material. Many vibrating Coriolis flow meters that generate pick off output signals from Coriolis deflections are capable of obtaining an output error of about 0.15% or less. However, in order to achieve this accuracy, interference of the Coriolis deflections are minimized. Although the above discussion addresses deflections in Coriolis flow meters, it should be understood that the deflections in other vibratory meters may be employed to measure parameters of the flowing material.
Vibratory meters are sometimes connected to other equipment that vibrates. For example, the pipelines the vibratory meters are connected to may be part of some equipment (e.g., semiconductor equipment, etc.). The equipment may have moving parts such as motors and pumps. These moving parts may impart a vibration to the equipment which in turn vibrates the pipelines connected to the vibratory meters. Moreover, the vibrations from the equipment may be imparted to the vibratory meters through means other than the manifold. For example, the vibratory meters may mount directly to the vibrating equipment which couples undesirable vibration to the flow tubes. Accordingly, the undesirable vibration in the pipelines or other parts of the equipment may transfer to the one or more flow tubes in the vibratory meter.
These undesirable vibrations may interfere with the Coriolis deflections which are used to measure the parameters of the material flowing through the flow tubes. This interference may increase the output error of the measurements of the flowing material. Increasing the output error in measurements of material is typically undesirable. Hence, there is a need to isolate a vibratory meter.